\begin{tikzpicture}
    \tkzDefPoints{0/0/O}
    \tkzDefPoint(180:1.5){A}
    \tkzDefPoint(0:1.5){B}
    \tkzDefPoint(130:1.5){C_1}
    \tkzDefPoint(90:1.5){C_2}
    \tkzDefPoint(40:1.5){C_3}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawSegments(A,B)
    \tkzDrawSegments(A,C_1  A,C_2  A,C_3)
    \tkzDrawSegments(B,C_1  B,C_2  B,C_3)
    \tkzDrawPoint(O)
    \tkzMarkRightAngle(A,C_1,B)
    \tkzMarkRightAngle(A,C_2,B)
    \tkzMarkRightAngle(A,C_3,B)
    \tkzLabelPoints[below](O)
    \tkzLabelPoints[left](A)
    \tkzLabelPoints[right](B)
    \tkzLabelPoints[left,yshift=.3em](C_1)
    \tkzLabelPoints[above](C_2)
    \tkzLabelPoints[right](C_3)
\end{tikzpicture}

